Electric induction furnace



Nov. 28, 1944.

W. RICHTER 2,363,994

ELECTRIC INDUCTION FURNACE I Filed NOV. 30, 1942 WaZherRzbher l INVENTOR. g/

Patented Nov.'2`8, 1944 UNITED STATES PATENT oFFlcE ELECTRIC INDUCTION FURNACE washer Richter, Whitefish my, wir., assigner to A. 0. Smith Corporation, Milwaukee, Wis., a corporation of New York Application November 30, 1942, Serial No. 467,310

' s calm. (c1. 21a-13) This invention relates to electric induction furnaces and constitutes an improvement upon the invention set forth and claimed in the cepending application of Eugene J. LimpeL Serial No. 453,004, iiled July 31, 1942, for Induction heating, and assigned to a common assignee with the present invention, which application issued to Patent No. 2,352,332 on June 27, 1944.

In the Limpel invention the heating of the tip of a partially closed nose of a bomb casing was made practical by employing a temporary core plug extending through the relatively small aperture in the nose and bridging the gap between larger members of the furnace core structure. 'Ihe temporary core plugs were applied individually to each bomb casing as it entered the furnace and were removed from the respective bomb casings as the latter were withdrawn. from the furnace. The plugs were then cooled and made ready for use in subsequent similar heating operations.

The present invention accomplishes the purpose of the plugs by the use of a long core member made a part of the furnace and disposed for' reciprocation during heating, the member passing through the aperture in the bomb casing and vthrough similar openings in the larger core elementsof the furnace. 'I'he reclprocation of the core member during heating prevents overheating of the same and provides a sustained flux heating currents in the metal immediately adjacent the aperture at the tip of the bomb casing.

The general object of the invention is to provide for the heating of the metal adjacent an aperture in a partially closed end of a tube by the use of a core member which isa part of the furnace structure and which thereby eliminates the labor and inconvenience attendant the use of individual core plugs for each heatclosed circuit for magnetic flux in the furnace.

Energizing coils encircle the position of the.

bomb casing 3 and serve to produce the magnetic i c iiux which induces the heating currents in the r:1.o path which more effectively induces the desired bomb casing. An auxiliary energizing coil S is disposed adjacent the tip of the bomb casing andencircles the aperture 'l in the nose of the bomb.

In carrying out the invention, a vertical opening 8 is provided centrally of the top of the outer core structure in alignment with the aperture 1. An axial bore 9 of a diameter similar to aperture 'I and opening 8 is provided in the upper end of the inner core structure l in alignment with the aperture 1. A reciprocating core member I0 is disposed vertically to extend through the opening l and aperture 1 and into the bore S.

The core member I ll is Aas'large in cross section as the aperture 1 will accommodate and preferably has only sufficient clearance in opening 8 and bore 9 togallow for the vertical reciprocation of the member during operation of the furnace. The member III is preferably suspended from above by suitable mechanism H adapted to reciprocate it up and down.

When the furnace is in operation, the core member Il.r serves to carry a heavy load of flux through aperture 'I from the top of the outer core structure I to the top of the inner core structure 4, and vice versa. 'I'he ux is more concentrated and dense in the member I0 than it is in the larger core elements, and this fact taken in addition to the proximity of the memgiven position, the member I0 loses itsability to carry as much ux and as a result its eilectiveness becomes diminished. However', by reciprocating it up-and down during4 operation of the furnace, the heating effect on the `core ,A

member Ill Vis spread over a substantial area and volume of metal, and undue heating is elimi- Y nated. The eiliciency of the member I0 to carry iiux is thereby kept at a maximum.

The invention is particularly. applicable where the size of aperture 1 is such as to require a max- The induction furnace illustrated comprises, 50 imum core section through theraperture and in general, an outer corestructure l enclosing energizing coils 2 and having its bottom open for receiving the partially formed nose of a bomb casing 3. The bomb casing is raised into the furnace by an elevator, not shown.

thereby substantially prohibits the employment of passages for cooling duid in the member l0. 'I'he core member may be cooled between successive operations of the furnace by applying a cooling medium externally to the member.

The entire core structure of the furnace including member it is laminated to avoid eddy current losses as much as possible. This also tends to prevent undue heating of the member it.

The core member lli should extend into 'the inner core structure Fi, at all times during operation or the furnace, a distance sufficient to give a substantially large surface area for transfer or iiux from one to the other so that saturation of the core member can be obtained.

The flux passing through the core member it induces heating current in the metal at the tip of the blank immediately surrounding the aperture l! and insures that this portion of the bomb casing will become heated as quickly as the remaining part through which the main portion or iiuir passes.

Various embodiments of the invention may be employed Within the scope of the claims.

The invention is claimed as follows:

l. in an induction furnace having an external stationary core member and primary energizing coils Jtherefor, a longitudinally movable central core member disposed to extend through an aperture in the article being heated and to carry hun 'between the relatively stationary core elements in all operative longitudinal positions of said member, and means to move said central core member longitudinally during the heating cycle of the furnace to prevent undue local heating of the member Without substantially altering the reluctance of the flux path.

2. ln an induction furnace having an external stationary core member and primary energizing coils therefor, a longitudinally movable central core member disposed to extend through an aperture in the article being heated and to carry @un between the relatively stationary core elements in all operative longitudinal positions of said member, and means to reciprocate said central core member longitudinally during the heating cycle oi the furnace to prevent undue heating of the member without substantially a tering the reluctance of the ux path.

S., in induction furnace for heating an electrically conductive article having an opening through which magnetic flux must pass for inducing heating current in the conductive material thereof adjacent said opening, said furnace comprising magnetic core structure including a longitudinally reciprocatory core section extending through said opening, coil means for magnetically energizing said core section, and means operative during the heating cycle of the furnace to reciprocate said core section longitudinally without substantially altering the reluctance of the iiux path in all of the operative positions of the core section, the length ofr the reciprocatory stroke imparted to said core section being .substantially less than the length of the core section and suicient to preclude said core section becoming injuriously overheated.

4. An induction furnace comprising magnetic core structure including angelongated longitudinally movable laminated core section designed to extend through an opening of small diameter in an electrically conductive article to be heated, stationary coil means for magnetically energizing said core section, and means operative While the furnace is on heat for imparting substantially continuous longitudinal movement to said core section without substantially altering the reluctance of the flux path in all of the operative positions of the core section for preventing the same from becoming locally overheated.

5. The method of preventing loss in efficiency of a portion of the core structure of an induction furnace where such portion is saturated with ux and disposed to receive substantial radiation of heat from the article being heated, comprising providing a separate core member of dimensions longer than the portion subjected to overheating, and moving such member longitudinally during the heating cycle of the furnace to present successive sections of said core member to the zone of maximum heat while maintaining a substantial area o iux transfer from said moving core member the remainder of the core structure of the furnace.

WALTHER RICHTER. 

